Hexanitrostilbene



United States Patent US. Cl. 260645 10 Claims The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to the preparation of a novel, thermally stable explosive material. More particularly, the invention is directed to 2,2,4,4',6,6-hexanitrostilbene (HNS) and preparation thereof.

In the past, nitro-substituted stilbenes have been prepared wherein the nitro group may be (1) on the alkene bridge, (2) on one or both of the aromatic groups or (3) on both the bridge and the aromatic groups. As an illustration of both (1) and (3), there is US. Patent No. 2,899,429 wherein a Schiff base is reacted with an arylnitromethane. Compounds exemplified by (2) have been prepared in the past by several methods. For example, by the condensation of 2,4,6-trinitrotoluene with benzaldehyde or nitrobenzaldehyde, one may obtain, respectively, trinitrostilbene and tetranitrostilbene. Further, by the direct nitration of stilbene, pentanitrostilbene may be obtained. The known methods of producing (2) are, however, characterized by very low yields and, in addition, are incapable of producing a stilbene having more than five symmetrically disposed nitro groups. This inability of known methods to prepare stilbenes having more than five aromatic nitro groups is apparently due to the deactivating influence set up as a result of the presence of the five nitro groups. As a consequence, the addition of further nitro groups was precluded.

It has now been found that a stilbene having six symmetrically disposed nitro groups, and characterized by the formula (NO RHC=CHR(NO wherein R=aromatic radical, may be prepared from (1) 2,4,6- trinitrotoluene (TNT) by reacting same with an aqueous solution of an alkali metal hypochlorite or alkaline earth metal hypochlorite or from (2) 2,4,6-trnitrobenzyl chloride by reacting same with an alkali metal hydroxide or alkaline earth metal hydroxide.

Accordingly, the objects of this invention are:

(1) The provision of 2,2,4,4,6,6'-hexanitrostilbene, a novel, thermally stable high explosive of military significance;

(2) The preparation of HNS;

(3) The preparation of 2,4,6-trinitrobenzyl chloride;

(4) The preparation of 2,2,4,4',6,6'-hexanitrobiben zyl;

(5) To provide a single process which, by suitable modification, may be used to prepare 2,4,6-trinitrobenzyl chloride, 2,2,4,4,6,6-hexanitrostilbene or 2,2',4,4,6,6- hexanitrobibenzyl and which is amenable to either batch, semi-continuous or continuous methods.

GENERAL CONSIDERATIONS The objects of this invention are accomplished by procedures consistent with the following reaction scheme:

OzN N02 i 3 I Deficiency of Excess of MeOCl MeOH MeO 01 NOz} CIIzC]. CHzCl J HNS HOl) TNBOI TNT anion) in situ MeOH) HNB HNS In the above-outlined reaction scheme, Excess of MeOCl is intended to signify that the TNT is added to the solution of metal hypochlorite (which normally contains a low concentration of metal hydroxide) and Deficiency of MeOCl-l-MeOH is intended to signify that the metal hypochlorite solution (with added metal hydroxide) is diluted with water and added to the TNT. The broken brackets are intended to signify that TNBCl is formed as an intermediate phase of the total reaction. The broken line beneath the brackets is intended to signify that the reaction may be shortstopped prior to formation of HNS to provide TNBCl.

In the prepartion of HNS, a solution of TNT in a solvent therefore is added, under instantaneous mixing conditions to an aqueous solution of metal hypochlorite, thereby creating an environment wherein there is an excess of hypochlorite. Apparently, the TNT is initially halogenated and the trinitrobenzyl chloride (TNBCl) thus produced reacts with metal hydroxide, which is normally present in hypochlorite solutions to form HNS. Thus, HNS may be obtained directly from TNT by this procedure.

The reaction may be shortstopped, with the concomitant formation of TNBCl, by drowning the reaction mixture with an acid, such as HCl, at the proper time (i.e. while the reaction is still in the TNBCl transition stage). Thus, TNBCl may be obtained from which HNS may be directly prepared by the addition thereto of a metal hydroxide such as NaOH.

In the preparation of HNB, an aqueous solution of a diluted, more alkaline hypochlorite is added gradually to the solution of TNT whereby an environment is created wherein the TNT anion is in excess. Initially, some of the TNT is apparently halogenated as in the preparation of HNS but, in the presence of excess TNT anion, the TNBCl formed is rapidly converted to HNB.

STARTING MATERIAL As set forth previously, the primary starting material is TNT. By addition of the TNT to the metal hypochlorite solution, either TNBCl or HNS may be obtained. By addition of the metal hypochlorite solution to TNT, HNB is obtained.

3 Alternatively, HNS may be prepared by using TNBCl as starting material and adding a metal hydroxide thereto.

THE HYPOCHLORITE The hypochlorite reactant may be an alkali metal or alkaline earth metal hypochlorite solution (which normally contains a very low concentration of an alkaline metal hydroxide) such as, for example, sodium hypochlorite, potassium hypochlorite or calcium hypochlorite. The alkaline metal hypochlorite is used as an aqueous solution having a metal hypochlorite concentration of from about l0%. No special purification of the hypochlorite is necessary and, in fact, commercially available hypochlorites may be used directly as bough Table 1, below, shows a few of the various hypochlorite agents which may be used according to the process of the invention.

TABLE I Of the reagents listed in Table 1, commercially obtainable Clorox is preferred because of ease of availability, low cost and good results. It is apparent, however, that any commercially available household bleach would produce equivalent results.

In the preparation of HNB, a diluted, more alkaline hypochlorite solution is used. In this circumstance alkaline metal hydroxide in addition to that normally present is added to the initial alkaline metal =hyprochlorite solution.

Although the use of the alkaline hypochlorite solu tions is preferred organic reagents, such as alkyl hypochlorites, may be used in lieu thereof. Alkyl hypochlorites, in particular, appear advantageous in that the large volume ratio of solvent-i-hypochlorite solution/ TNT is reduced by the use thereof. Tertiary butyl hypochlorite is illustrative of the organic hypochlorites which may be used.

THE SOLVENT SYSTEM The solvent should be one which will dissolve TNT (e.g. tetrahydrofuran) at ambient temperatures and below and which, with the addition of a lower aliphatic alcohol such as ethanol or methanol, will provide a homogeneous solution with an alkaline metal hypochlorite. Although tetrahydrofuran is the preferred solvent, p-dioxane, diglyme and acetonitrile may also be used.

When used with the preferred hypochlorite reagent (i.e. 5% Clorox) a large volume of solvent is needed per unit of HNS produced, since the requirements for a homogeneous reaction are:

TNT-1 g.

THF ml. CH OH5 ml.

5% Clorox-10 ml.

TEMPERATURE The reaction may be run at temperatures ranging from about 0 C. and below to ambient temperature and above. For example. in a THF-methanol system which was started at room temperature, the reaction mixture reached a maximum temperature of about 50-60 C. with a yield of about 25% of theoretical being obtained. The yield gradually increases with decreasing temperature until a yield of HNS of about 45% of theoretical is attained at about C. and below. At temperatures of below about 10 C., unreacted TNT will tend to crystallize, thus slowing the rate of reaction somewhat.

After the initial reaction (i.e. formation of the intermediate TNBCl), the temperature may be raised and heating will, in fact, hasten crystallization of the product.

The following specific embodiments will more fully illustrate the process of the invention. It is to be understood, however, that the following examples are merely illurative and are not intended as limitations of the scope of the invention.

EXAMPLE I This example illustrates the small scale preparation of 2,2,4,4',6,6-hexanitrostilbene by the reaction of trinitrotoluene and NaOCl.

A solution of 10 g. of TNT in 100 ml. of tetrahydrofuran and 50 ml. of methanol was chilled to 0 C and then added quickly, with thorough mixing, to 100 mi. of 5% aqueous NaOCl which was also chilled to 0 C. The reaction temperature was held at about 15 C. Within two minutes, fine crystals appeared in the reaction mixture. The mixture was allowed to stand until precipitation of the crystalline product was complete. The product was then filtered ofi and the filter cake was washed with methanol until the washings were colorless and then dried in an oven at 100 C. The HNS obtained weighed 4.2 g. (42% of theoretical) and was further purified by slurrying with refluxing acetone for two hours, filtration and drying in vacuo at 100 C. There was obtained 2,2,4,4',- 6.6-hexanitrostilbene, designated as Grade I, as a very fine cream colored crystalline material having a mol. wght. of 450.3 and melting at 313-315 C. Recrystallization from nitrobenzene or dimethyl formamide yielded pale yellow needles which melted at 316 C. Identification was authenticated by X-ray powder diffraction patterns and infrared spectra.

Table 2, below, illustrates a comparison of some of the properties of HNS, Grade I with recrystallized HNS:

EXAMPLE II This example illustrates the preparation of TNBCl by shortstopping the HNS reaction of Ex'. I.

The reaction was carried out exactly as in Ex. I, above, except the reaction was stopped after one minute by drowning the reaction mixture in about one liter of water containing 10 ml. of concentrated HCl. A cloudy, yellow mixture was formed from which trinitrobenzyl chloride, as a waxy crystalline material, began to separate almost immediately. After about one hour, precipitation was complete and the TNBCl was filtered 01f, washed with water and dried. There was obtained 10 g. of theoretical) of TNBCl having a melting point of 85 C. upon recrystallization from benzene-hexane. Identification was authenticated by infrared spectra.

Although HCl is used inthis example, any acid, whether organic or inorganic, will shortstop the reaction.

EXAMPLE III This example illustrates the large scale preparation of HNS to demonstrate feasibility of contigous flow production.

Apparatus: A 500 ml., 3-neck, jacketed, round bottom flask with a stopcock at the bottom was suspended so that the stopcock drained into a glass funnel. The funnel was connected to a coil of glass tubing suspended in a cooling bath of ice and water and arranged to deliver into a large Erlenmeyer flask. The jacketed flask was cooled to 12 C. with ice cooled water by means of a circulating pump. A mechanical stirrer with a one inch polyethylene disc in place of a stirring blade was inserted in the flask so that in operation the liquid dropping on the disc would be distributed from it as a thin layer on the upper portion of the cooled section of the flask. The tips of two dropping funnels were adapted to dispense liquid onto the disc.

Procedure: A solution of 100 g. TNT in 1 liter of THF and 500 ml. methanol was prepared and dispensed from one dropping funnel while 1 liter of 5% aqueous sodium hypochlorite (Clorox) was dispensed from the other funnel. The flow of the solutions was regulated to provide 1.5 ml. TNT solution per 1.0 ml. of NaOCl solution and also to be certain that the dwell time in the cooled coil was at least one minute in order to allow halogenation of the TNT to be completed during cooling. The reaction mixture was allowed to stand in the receiving flask for two hours (i.e. until precipitation of the crystalline HNS was complete). This precipitation time may be shortened to 30 minutes, with no loss in yield, by warming the flask in a water bath at 40 C. The product was then filtered off, washed with methanol and dried. The yield of HNS, Grade I weighed 42 g. (42% of theoretical).

EXAMPLE IV This example illustrates the preparation of HNS from TNBCl and alkali.

A solution of 2.6 g. (0.01 mole) of trinitrobenzyl chloride in 40 ml. of THF and 20 ml. methanol was prepared in a small flask. To this solution, at ambient temperature, was added 40 ml. water containing 0.4 g. (0.01 mole) NaOH. Within /2 minute HNS, as a fine crystalline precipitate, appeared in the solution. The mixture was allowed to stand for 15 minutes and then filtered. The filter cake was then washed with methanol until the washings were colorless and dried in an oven at 100 C. There was recovered 1.12 g. HNS (50% of theoretical) which, when recrystallized from nitrobenzene, formed fine yellow needles which melted at 315-316 C.

EXAMPLE V This example illustrates the preparation of HNB by the reaction of TNT and a solution of 5% NaOCl containing added NaOH.

A solution of g. TNT in 50 ml. THF and 100 ml. of methanol was prepared in a 500 ml. wide mouth Erlenmeyer flask equipped with a mechanical stirrer and a 125 ml. dropping funnel. A solution prepared by adding 35 ml. of 5% aqueous sodium hypochlorite to 0.5 g. NaOH dissolved in 65 ml. water was placed in the dropping funnel and added, with rapid stirring during a period of 5-10 minutes, to the TNT solution. After about one minute there appeared HNB as a crystalline material. By the end of the addition of the hypochlorite solution the temperature of the reaction mixture had risen to 35 C. The mixture was allowed to stand for minutes and then filtered. The filter cake was washed with methanol and dried. There was obtained 7.9 g. of HNB (79% of theoretical) melting, after recrystallization from hot acetone, at 218-220" C. Identification was authenticated by infrared spectra and X-ray powder diffraction patterns.

EXAMPLE VI This example illustrates a semi-continuous method for the production of HNS from 5 aqueous sodium hypochlorite and TNT in THF-methanol.

Apparatus: A 12-liter, 3-neck round bottom flask was equipped with a 0.5 in., I.D., outlet tube at the bottom to permit rapid discharge of the reaction mixture. The flask was then suspended in a cooling bath with the outlet extending through a rubber stopper in the bottom of the bath. The flask was equipped with a mechanical stirrer and two funnels, with 10 mm. bore stopcocks to permit rapid flow, for dispensing reacting solutions into the flask. The cooling bath was filled with ice and water 6 and a propeller type metal stirrer was used to keep the bath stirred.

Reaction solutions: (a) 5% aqueous sodium hypochlorite and (b) a solution of 500 g. TNT in 5 liters of THF+2.5 liters of methanol.

Procedure: Enough NaOCl solution was added to the flask to fill the outlet tube (i.e. about 40 ml.), since this portion would not be expected to be mixed in the initial charge. Then 250 ml. of 5% aqueous NaOCl was added as rapidly as possible, rapid stirring was begun and 400 ml. of TNT solution was added rapidly to the NaOCl solution. The mixture was stirred for one minute and then run out of the flask as rapidly as possible (i.e. about 6 sec.). into a large container. The outlet tube was not emptied (i.e. the reaction mixture was discharged just to the bottom of the flask each time). The flask was then recharged with portions of NaOCl and TNT solutions and the cycle was repeated until all of the TNT solution had been used (i.e. 20 charges in 31 minutes of elapsed time). The reaction mixture was collected and allowed to stand for two hours and then filtered on large Buchner funnels. The filter cakes were then washed well with methanol and dried. An amount: of HNS weighing 230 g. (46% of theoretical) was obtained.

HNS is a high explosive capable of withstanding high temperature for prolonged periods and is thus of great utility to the government for spacecraft applications. For example, HNS has been combined. with Dipam in the fabrication of MDP (Mild Detonating Fuse) for application in missile and spacecraft stage separation.

PBX powders have been prepared from both HNS Grade I and recrystallized HNS.

In the preparation of the PBX powders, Teflon was used as a binder in the ratio of /5, HNS/Teflon. At C. and 20,000 p.s.i. the PBX containing HNS Grade I was preseed to high density, 98% TMD, while the recrystallized HNS-PBX was pressed to 96-97% TMD. The impact sensitivity of the PBX molding powder was in the same range at Tetryl and the thermal stability of the PBX was 0.98 cc./g./hr. at 260 C.

Table 3, below, shows some of the comparative properties of HNS as against such widely used military explosives as Tetryl and CH6.

l Decomposed.

The powder or output of HNS is about equal to that ,of Tetryl but below that of CH-6.

From Table 3 it is seen that HNS out performs both Tetryl and CPI- 6 in high temperature applications.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent of the United States is:

1. The compound 2,2',4,4,6,6'-hexanitrostilbene characterized by the following structural formula:

N0 OzN 2. The method of preparing 2,2',4,4,6,6-hexanitrostilbene which comprises adding a solution of 2,4,6-trinitrotoluene in a solvent therefor to an aqueous solution of an alkaline metal hypochlorite and recovering the resulting product.

3. The method of claim 2 wherein said solvent is a mixture of tetrahydrofuran and methanol.

4. The method of claim 2 wherein the initial reaction temperature is maintained at a temperature below about 15 C.

5. The method of claim 2 wherein said alkaline metal hypochlorite is selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. I

6. The method of preparing 2,2',4,4',6,6'-hexanitrobibenzyl which comprises adding an aqueous solution of alkaline metal hypochlorite containing an alkaline metal hydroxide to a solution of 2,4,6-trinitrotoluene in a solvent therefor and recovering the resultant product.

7. The method of claim 6 wherein said alkaline metal hypochlorite is selected from the group consisting of sodium hypochlorite, potassium hypoehlorite and calcium hypochlorite.

8. The method of claim 6 wherein said alkaline metal hydroxide is sodium hydroxide.

9. The method of claim 6 wherein said solvent is a mixture of tetrahydrofuran and methanol.

10. The method of claim 6 wherein the temperature is maintained below about 15 C.

References Cited UNITED STATES PATENTS 8/1966 Shipp 260-646 OTHER REFERENCES LELAND A. SEBASTIAN, Primary Examiner US. Cl. X.R. 

1. THE COMPOUND 2,2'',4,4'',6,6''-HEXANITROSTILBENE CHARACTERIZED BY THE FOLLOWING STRUCTURAL FORMULA:
 2. THE METHOD OF PREPARING 2,2'',4,4'',6,6''-HEXANITROSTILBENE WHICH COMPRISES ADDING A SOLUTION OF 2,4,6-TRINITROTOLUENE IN A SOLVENT THEREFOR TO AN AQUEOUS SOLUTION OF ALKALINE METAL HYPOCHLORITE CONTAINING AN ALKALINE METAL HYDROXIDE TO A SOLUTION OF 2,4,6-TRINITROTOLUENE IN A SOLVENT THEREFOR AND RECOVERING THE RESULTANT PRODUCT. 